aas1973

So I picked up a used dynamite mach .15. Can get it running fairly easy enough now that i've figured some things out but here is my dilemna...
When I try to set the idle speed screw in to prevent the carb from closing off when I hit the brake I can't get the damn thing to start.With the screw looseI run smooth until and unless I try to slow down/brake (or crash secondary to not braking).
Any suggestions/help would be greatly appreciated.
Thanks,
Alan

rendezvous944

The carb has to be slightly open or engine will shut off. The engind needs a certain RMP to stay running. You need to set the engine to the lowest setting it will stay running and adjust your brake to be slightly engaged or dragging. Once you hit the trrottle the brake will release. Also adjust your EPA if you have them so you can adjust the max/min carb opening and brake closesettings.

aas1973

EPA?
If Iam not mistaken.The idle screw (to which I was referring) is responsible for making sure that the carb doesn't close off when the throttle is let go of or reversed(ie for braking).As the screw is tightened, the minimum throttle aperature increases does it not? Is there some other function that I am missing?
Thanks
Alan

Argess

What you are decribing seems almost impossible. Having the carb a bit more "open" should not make it more diffiuclt to start. Quite the opposite I would think.

If it is indeed the case, you may have an air-leak. With carb closed, you are getting some air from the leak and fuel from the HSN. Opeing the carb up adds too much extra air and it won't be rich enough to start. Look for a loose carb to block. RTV as required.

On the other hand, and I mean no offense.....are you certain you don't have the screws mixed up and are adjusting the LSN vs the throttle stop screw?

aas1973

No offense taken.  I am positive that I've got the throttle stop screw.  I had orignally thought it might be an air leak as well however I don't seem to have any trouble running at higher RPM/throttle once started.  I'll reseal and see if it helps just the same.  Appreciate the input.

Argess

Air leaks are less of a problem at higher speeds as the amount of air leaking is then small compared to the amount coming through the carb. Please post what you find when you fix it. It's an interesting problem.

rider313

how is the pinch on the motor?

aas1973

Compression doesn't seem too bad.  Going to seal backplate and around carb and see what happens.

authorjim1

I agree with all said, but even though the idle screw sets the opening, the linkage must be set so that it does not try to close it under braking. The springs on the linkage and the set screws allow adjustment of that a bit. With the air filter off make sure you are not closing the opening when you hit the brake. Sometimes if the linkage pushs hard against the stop it will stick. Also try to rebalance the LSN and the Idle screw. A littl richer on the LSN and after all runs fine then readjust the idle.


Hope this helps

Jim

aas1973

This is exactly what is happening.When braking, the carb is getting closed (more than I would like).I can adjust the idle speed screw to prevent this from happening, however when I do so, the engine will not start.
Thanks again.

rider313

how high are you setting your idle? I dont see why it wouldnt start after you set you idle? I think your problem is eslewhere. Is the motor warm or cold when you do the restart?

aas1973

I don't get it either. I have the carb open just a bit. Starts fine at that setting as long as the idle screw is loose (I don't have to play with the throttle at all). When I try to set the idle screw to prevent the throttle from closing any further, no luck, won't start (neither warm nor cold). I don't have it open any wider (nor any less open) than when the screw is loose. It just doesn't seem to make any sense.

rider313

are you tightening the right screw? It should be the one that sticks out a like a 45* angle by the carb throut. Not the one with a brass sleeve or the one set in the end of the carb body.

aas1973

I definately have the right screw.  To be honset I'm just glad to see that other people seem to be surprised by this too.  Of course I would prefer to figure out a solution but it's nice to know I'm not necessarily a total idiot.

rider313

ya you got me beat on this one. Go through a checklist on parts such as glow plugs ext.

image079

There is too much end play in the carby shaft. Some carby's have a spring inside to push the carby shaft in against the idle screw.
With my carby (rotary) when I push on the end of the carby shaft, it moves slightly in , but the spring pushes it back. If I push it in while
the engine is running and hold it there, the engine stalls.

aas1973

Don't know what it was but after taking the thing apart, cleaning the carb, resealing the engine, works like a charm.  Thanks for the input.